10-chloro-phenoxaphosphine and 10-bromo-phenoxaphosphine are important intermediates in the synthesis of metallo-organic complexing ligands as well as in the synthesis of phenoxaphosphinic acids. Complexing ligands form an essential component of the catalyst system in homogenous catalysis. Phenoxaphosphine derivatives are used as subunits for complexing ligands in a multiplicity of catalytic reactions, such as hydroformylations, hydrogenations, hydroxycarbonylations, alkoxycarbonylation or allylic alkylations, wherein, to some extent, extremely high selectivities can be attained with simultaneous high conversions and turn-over frequencies of the catalyst system. Thus, Hobbs et al describes in J. Org. Chem., Vol. 46, 4424 (1981), the asymmetric rhodium-catalyzed hydroformylation of vinyl acetate using a DIOP derivative as a ligand which contains two phenoxaphosphine subunits.
From the literature, processes are already known for the production of 10-chloro-phenoxaphosphines. Freedman et al describes in J. Organ. Chem. 1961, Vol 26, 284 the conversion of p-tolyl ether with phosphorus trichloride and aluminum trichloride. After the aqueous processing, the reaction product was identified as 2,8-dimethyl-phenoxaphosphinic acid. The 2,8-dimethyl-phenoxaphosphinc acid can be converted analogously to the teaching of Hellwinkel and Krapp in Chem. Ber. 1978, Vol 111, 13 for dibenzophosphoric acid by reaction with phosphorus oxychloride at 200xc2x0 C. and subsequent reaction with red phosphorus at 180xc2x0 C. to form 10-chloro-2,8-dimethylphenoxaphosphine. The synthesis from ether is thus a three-stage synthesis and the total yield is 59.6% over all stages. Thus, an economical production of the compound is not possible.
It is an object of the invention to provide an economical process to prepare substituted 10-chloro-phenoxaphosphines or the corresponding substituted 10-bromo-phenoxaphosphines in high yield and purity in a technically simple manner.
This and other objects and advantages of the invention will become obvious from the following detailed description.
The process of the invention for the preparation of substituted 10-chloro-phenoxaphosphines and 10-bromo-phenoxaphosphines comprises reacting a substituted diphenyl ether with a phosphorus trihalide in the presence of at least one Lewis acid and reacting the resulting product with an amine to produce the substituted 10-halo-phenoxaphosphine.
It has surprisingly been found that the addition of amines for a multiplicity of substituted 10-chloro-phenoxaphosphines and 10-bromo-phenoxaphosphines, which will be referred to in the following as 10-halogen-phenoxaphosphines, permits carrying out the reaction in a single stage under mild conditions with low yield losses. Through the addition of amines, the intermediately formed complex of substituted 10-chloro-phenoxaphosphine and metal chloride or of substituted 10-bromo-phenoxaphosphine and metal bromide can be cleaved under conditions in the absence of water, whereby the hydrolysis of the substituted 10-halogen-phenoxaphosphines (halogen=Cl, Br) to the free acid is prevented. The conversion is illustrated in the following scheme. 
The substituents of the 10-halogen-phenoxaphosphines of formula (II) and the diphenyl ether (I) used as the starting compound can be varied over a wide range. Thus, R1, R3, R4, R5, R6 and R8 are independently selected from the group consisting of hydrogen, alkyl and alkoxy of 1 to 22 carbon atoms, acyloxy of 1 to 22 carbon atoms, alkylthio of 1 to 22 carbon atoms, dithioacyloxy of 1 to 22 carbon atoms, aryloxy of 6 to 18 carbon atoms, arylthio of 6 to 18 carbon atoms, phenyl, fluorine, chlorine, bromine, iodine, xe2x80x94NO2, CF3SO3xe2x80x94, xe2x80x94CN, HCOxe2x80x94, RSO2xe2x80x94, RSOxe2x80x94, dialkylamino of 1 to 8 alkyl carbon atoms, AlKxe2x80x94NHCOxe2x80x94, AlKCOxe2x80x94, AlKxe2x80x2COOxe2x80x94, HCOxe2x80x94NHxe2x80x94, benzoyl, benzoyloxy, AlKxe2x80x2COOxe2x80x94CHxe2x95x90CHxe2x80x94, Ar2POxe2x80x94, AlK is alkyl of 1 to 4 carbon atoms, AlKxe2x80x2 is alkyl of 1 to 8 carbon atoms, Ar is phenyl unsubstituted or substituted with at least one alkyl of 1 to 4 carbon atoms, R2 and R7 are individually selected from the group consisting of alkyl and alkoxy of 1 to 22 carbon atoms, alkylthio of 1 to 22 carbon atoms, dithioacyloxy of 1 to 22 carbon atoms, aryloxy of 6 to 18 carbon atoms, arylthio of 6 to 18 carbon atoms, phenyl, fluorine, chlorine, bromine, iodine, xe2x80x94NO2, CF3SO3xe2x80x94, xe2x80x94CN, HCOxe2x80x94, RSO2xe2x80x94, RSOxe2x80x94, dialkylamino of 1 to 8 alkyl carbon atoms, AlKxe2x80x94NHxe2x80x94COxe2x80x94, AlKCOxe2x80x94, AlKxe2x80x2COOxe2x80x94, HCOxe2x80x94NHxe2x80x94, benzoyl, benzoyloxy, AlKxe2x80x2COOxe2x80x94CHxe2x95x90CH and Ar2POxe2x80x94. X is chlorine or bromine.
Preferably, R1, R3, R4, R5, R6 and R8 are individually selected from the group consisting of hydrogen, alkyl and alkoxy of 1 to 22 carbon atoms, acyloxy of 1 to 22 carbon atoms, aryloxy of 6 to 18 carbon atoms, phenyl, fluorine, chlorine, bromine, xe2x80x94NO2, xe2x80x94CN and CF3SO3xe2x80x94. R2 and R7 are preferably individually selected from the group consisting of alkyl and alkoxy of 1 to 22 carbon atoms, acyloxy of 1 to 22 carbon atoms, aryloxy of 6 to 18 carbon atoms, phenyl, fluorine, chlorine, bromine, xe2x80x94NO2, xe2x80x94CN and CF3SO3xe2x80x94.
More preferably, R1, R3, R4, R5, R6 and R8 are individually selected from the group consisting of hydrogen, alkyl of 1 to 22 carbon atoms, phenyl, fluorine, and chlorine. X is preferably chlorine.
Compounds in which R2 and/or R7 are hydrogen, are not suitable for this reaction, since, in this case, a bond linkage with the inclusion of the phosphorus atom, can also occur in the para position to the ether bridge. The products formed herein lead to phosphorus-bridged chains formed through intermolecular reaction instead of to substituted 10-chloro-phenoxaphosphines which are formed by intramolecular cyclization.
The conversion of (I) with the phosphorus trihalide in the presence of at least one Lewis acid is carried out at a temperature of 0 to 200xc2x0 C., preferably 0 to 150xc2x0 C. and especially preferred at 50 to 120xc2x0 C. While, according to the process, it is possible for the invention to use a phosphorus halide and a Lewis acid with different halogen substituents, this can lead to the formation of a mixture of bromo and chloro derivatives due to halogen exchange reactions.
The process of the invention is generally carried out at pressures of 0.1 to 2 MPa but it is preferred to conduct the reaction at atmospheric pressure. Conversions at increased pressure serve essentially for raising the boiling point of the optionally used solvent to be able to set the optimum reaction temperature.
To reach complete conversion, at least a stoichiometric equivalent of the phosphorus halide must be added to the substituted diphenyl ether. Markedly excess quantities are not detrimental. They are suitably distilled off, together with an optional solvent, after the completion of the reaction and before addition of the amine. Excess quantities of the phosphorus halide can serve as a further solubilizer or as complete replacement of an inert solvent.
Examples of Lewis acids are halides of main group III, as well as of subgroups VIII, I, and II of the periodic system of elements. Particularly preferred are zinc halides, copper halides, iron halides and aluminum halides. Especially preferred are zinc-II-chloride, copper-II-chloride, aluminum trichloride, aluminum tribromide, and iron-II-chloride. The Lewis acids can be used in the form of the pure salt as well as on substrate materials, such as silica gel.
To carry out the process of the invention, the Lewis acid is usually added to the diphenyl ether in a molar excess of up to the 1.5-fold. While greater excess quantities are possible, it is not useful for reasons of economy and ecology. Preferred is a molar excess of up to 1.2-fold of the Lewis acid and especially preferred is a maximally equimolar use of the Lewis acid relative to the diphenyl ether. However, it is also possible to use the Lewis acid in a lesser quantity than that stoichiometrically required.
It has surprisingly been found that already at a molar ratio of Lewis acid to diphenyl ether of 0.7: 1, yields of 80% of 10-halogen-phenoxaphosphine of formula (II) are obtained.
The reaction can be carried out with or without a solvent. Suitable solvents are aliphatic ethers and inert hydrocarbons. As examples of aliphatic ethers and inert hydrocarbons are toluene, tetrahydrofuran, diethyl ether, hexane, cyclohexane, pentane and benzene. The amount of solvent is selected so that the concentration of diarylethers is 0.1 to 80 percent by weight. The reaction is preferably carried out without solvents.
The complex of 10-halogen-phenoxaphosphine and the Lewis acid is cleaved by adding an amine after completion of the reaction. Preferred for this purpose are trialkylamine of 3 to 12 carbon atoms, a mixed tertiary alkylarylamine of 8 to 22 carbon atoms, an alicyclic amine of 4 to 8 carbon atoms with an optional oxygen as a further heteroatom, or a heterocyclic amine of 4 to 22 carbon atoms. Examples are trimethylamine, triethylamine, tri-n-butylamine, N,N-dimethylaniline, pyridine, xcex1-picoline, morpholine, piperidine, and quinoline. Especially preferred amines for setting free the 10-halogen-phenoxaphosphine are triethylamine and pyridine.
The amines are in general added to the reaction mixture in amounts of 0.5 to 5 molar equivalents, preferably 0.9 to 3, and more preferably 1 to 2.5 molar equivalent, relative to the Lewis acid. Depending on their state of aggregation, the amines can be used in the form of the pure liquid or the pure solid.
Cleaving the complex of 10-halogen-phenoxaphosphine and Lewis acid is carried out at a temperature of xe2x88x92100 to 100xc2x0 C., preferably at xe2x88x92100 to 50xc2x0 C., more preferred at xe2x88x9250 to 25xc2x0 C.
The 10-halogen-phenoxaphosphine is subsequently extracted with a solvent. After filtering off the separated Lewis acid-amine adduct and removing the solvent from the filtrate, the 10-halogen-phenoxaphosphine remains as a solid or an oil. Possible solvents which can be used are aliphatic ethers and inert hydrocarbons. Examples of aliphatic ethers and inert hydrocarbons are toluene, tetrahydrofuran, diethyl ether, hexane, cyclohexane, pentane and benzene.